as far as software i would like an android based carputer just for google maps,the live wallpaper named audio glow, and a music player like poweramp or anything that has crossfade.
but iam willing to use windows as long as i can get the same effect.

so what do you all think is it doable? and if it is where do i start as i have no experience with cars but plenty with computers.

That's too bad you still haven't gotten any replies to this thread. If you're looking for something that can just do the features you named, you'd be much better off going the android route. Seeing as it can handle all those things easily with off the shelf apps, you're golden. Throw a niece frontend on it and you're good to go. Also since tablets are battery powered the power supply issues are trivial. No moving parts to go bad or make noise, and a ton of useful sensors. Not to mention you'll accomplish the build for 1/5th of the price of a full blown pc. For a super slick build, make it dockable and motorized. There's a number of examples on youtube.